But requiring higher integration of renewables poses problems for the power grid. Wind and solar power, for example, have problems with intermittency. That is, solar production slows when the sun doesn’t shine and wind lags when the breeze doesn’t blow.
To make up for that, grid managers such as the California Independent System Operator have to rely on other energy sources while ramping up and down over the course of the day and night to meet sharp changes in electricity net demand.
Natural gas frequently fills in the gaps but energy storage systems can also be used.

The San Diego County Water Authority wants to find somebody to develop an energy storage facility at the San Vicente Reservoir, nestled among the Cuyamaca Mountains near Lakeside.

And officials are not only confident they can find a number of potential candidates willing to fully develop the project, they expect to entertain proposals in the range of $1.5 billion to $2 billion.

“That’s depending on the size of this facility and the configuration,” said Kelly Rodgers, the energy program manager for the Water Authority, which is working in partnership with the City of San Diego on the project. “This would be a great opportunity.”

The authority has sent out a formal request for proposals – called an RFP – to entities interested in putting together what officials call a “full-service team” that would not only design and construct a hydro energy storage facility at San Vicente but also fund, operate and maintain the project.

Water officials also expect the storage facility to better integrate renewable energy sources into the electric grid and help stabilize water prices for San Diego ratepayers.

“Folks might ask, hey, why is our water agency involved in energy?” Rodgers said. “As trite as it may seem, there truly is a water-energy nexus.”

While solar arrays and wind farms are renewable projects most people are familiar with, pumped hydro facilities have actually been part of the nation’s energy grid for more than 100 years.

The concept is pretty basic: Using turbines, water is pumped from one reservoir up to another and then released, with the ensuing rush of water generating electricity.

In fact, the authority already has a pumped storage facility up and running.

Opened in 2012, a facility at Lake Hodges has a two-turbine pump house that sends water uphill from the city-owned Hodges Reservoir to the authority’s Olivenhain Reservoir, generating some 40 megawatts of energy on demand.

But authority officials expect the San Vicente project to be more than 10 times larger than the Lake Hodges facility – up to 500 megawatts.

At full capacity, the project would generate up to eight hours of stored energy, enough to supply about 325,000 homes annually, and could be completed as early as 2025.

The money from the entity that eventually is selected to build the project is expected to put some downward pressure on ratepayers’ water bills.

“Our main mission is to provide core services,” Rodgers said. “And this is an excellent opportunity for us to be able to potentially gain additional revenue that would help to offset our operational costs and sustain our water rates.”

The project’s other selling point relates to state and local policies mandating reductions in greenhouse gas emissions and boosting clean-energy sources.

California already has a Renewables Portfolio Standard that calls for 50 percent clean energy by 2030 and there is legislation in Sacramento calling for boosting that all the way to 100 percent by 2045.

In addition, the City of San Diego’s Climate Action Plan calls for 100 percent of the city’s energy coming from renewable sources and cutting the city’s greenhouse gas emissions in half by 2035.

But requiring higher integration of renewables poses problems for the power grid. Wind and solar power, for example, have problems with intermittency. That is, solar production slows when the sun doesn’t shine and wind lags when the breeze doesn’t blow.

To make up for that, grid managers such as the California Independent System Operator have to rely on other energy sources while ramping up and down over the course of the day and night to meet sharp changes in electricity net demand.

Natural gas frequently fills in the gaps but energy storage systems can also be used.

Lithium-ion battery storage has received a lot of media attention of late but pumped hydro fits the bill as well.

“San Vicente sits in a location that is really just optimal,” said Rodgers. “There is so much existing infrastructure in place” for a pumped hydro project.

The water, of course, is already there. The San Vicente Reservoir holds up to 247,000 acre-feet of water. One acre-foot provides enough water supply for two families of four annually.

And the site sits near interconnection points to the grid. Power generated at the San Vicente facility could be delivered via electrical lines parallel and interconnected to San Diego Gas & Electric’s Sunrise Power Link.

The team eventually selected for the project would have to design and build a number of pieces of infrastructure.

An upper reservoir would have to be created. Authority officials estimate the upper reservoir would hold fewer than 7,000 acre-feet of water and consider a spot about a half-mile north of San Vicente as a potential site.

A tunnel system and an underground pump house would connect the two reservoirs. The pump house would likely contain four 125-megawatt, reversible pump-turbines capable of lifting water to the upper reservoir and generating power as it flows down.

When supplies of wind and solar energy exceed demand, water could be pumped to the upper reservoir and stored for later use. During periods of peak energy demand, water would flow down to generate carbon-free power.

“Pumped storage is like a big battery,” Rodgers said. “Imagine that the battery is sitting between where energy comes into the region and where energy is needed in the region.”

The stored up energy is then used to respond quickly to peak demand on the grid.

It takes energy to send water uphill. According to the California Energy Commission, about 4- kilowatt-hours of energy is consumed during pumping for every 3-kilowatt hours that is generated. As a result, electric utilities with pumped storage plants tend to call them into service when on-peak electricity prices are 30 percent higher than during off-peak hours.

Rodgers said the proposed project at San Vicente’s real value comes from its ability to store power.

”Pumped storage is really a project that uses more energy than it produces so the benefit of pumped storage is being a big battery, not as an energy generation plant,” Rodgers said. “It’s purely for the storage, and being able to respond quickly to peak demand on the grid.”

The authority says the project would be a closed-loop system, would not consume water or interfere with the existing water supply, water quality, fisheries or recreational activities at San Vicente.

Officials are confident the project will attract interest. In March, the authority said 18 entities responded to preliminary solicitations to build the pumped storage facility.

Rodgers would not identify the parties but said the project attracted “significant interest internationally, nationally and locally.”

The RFP deadline is Sept. 12 and Rodgers said the city and the authority will narrow down the proposals, compile a short list of candidates, discuss terms and conditions and hope to have an agreement in place by next March.

Gary Ackerman, executive director of the Western Power Trading Forum, an organization based in Sacramento whose 90 members in the West buy and sell power, does not know the details of the San Vicente project but said he likes the idea behind it.

“It makes a lot of sense,” Ackerman said. “If the state is serious about implementing a lot of renewables into the energy portfolio, and managing that effectively so you reduce greenhouse gas emissions, pumped storage is the way to go.”

Some environmentalists have expressed concerns over large pumped hydro projects, citing potential impacts on habitat and groundwater.

“We’re focused on 100 percent renewable energy and storage is a real important part of that,” said Sarah Friedman, senior campaign representative for the Sierra Club.

At the same time, Friedman said the Sierra Club needs to look at more details before passing judgment on the proposed San Vicente project.

“I think its location on the grid is really interesting,” Friedman said. “But it’s in the very early stage of the environmental permitting so we definitely don’t have a position on it at this time. We need more information.”

Through a partnership between the authority and the city, the dam at San Vicente was recently raised 117 feet, adding 152,000 acre-feet to the reservoir’s capacity as part of an emergency storage project to make sure water is available to the San Diego region even if access to imported water supplies is interrupted.

The effort took eight years to complete before San Vicente was reopened to boating and fishing in 2016.

The City of San Diego retains ownership of the original storage capacity of the reservoir while the Water Authority owns San Vicente’s new, additional storage capacity for regional use.

The two agencies share the cost of operating and maintaining the dam and reservoir.

According to the California Energy Commission, there are four “true” pumped storage power plants in the state, including Lake Hodges, that possess reversible turbines.

The CEC says there are five other pumping-generating plants in California but they are not used to meet utility peak loads of an electric grid.

At an estimated 500 megawatts, a San Vicente project would trail only the pumped storage facilities at Castaic Lake in Los Angeles (1,682 megawatts) and the Helms project in Fresno County (1,212 megawatts) in size.

However, a proposed pumped storage plant near the Joshua Tree National Park called Eagle Mountain is listed with capacity for 1,300 megawatts. Developers of the project, which would use two excavated pits from a retired mining operation as reservoirs, want the project to come online by 2023.

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

The copyright of this article is owned by the author or publisher indicated. Its availability here constitutes a "fair use" as provided for in section 107 of the U.S. Copyright Law as well as in similar "fair dealing" exceptions of the copyright laws of other nations, as part of National Wind Watch's noncommercial effort to present the environmental, social, scientific, and economic issues of large-scale wind power development to a global audience seeking such information. For more information, click here. Send takedown inquiry or request to excerpt to query/wind-watch.org. Send general inquiries and comments to query/wind-watch.org.